Yep....distilled water and water wetter = 160 deg in my souped up flathead !! Even in nasty hot weather in ambient 105+ temps, it didint get over 190. Rat
So distilled water is the ticket.I just went down to Summit and bought a can of 40 Below,it states on it that distilled is the way to go.
I use WW in all my old stuff, mixed with distilled water. It really works great on stock Model Ts with no water pump. It stops the formation of steam pockets. Once you get steam it stops cooling and just makes more steam and then boil over and then.......!